Exploring Low-Grade Iron Ore Beneficiation Techniques: A Comprehensive Review

Abstract

The beneficiation of low-grade iron ores is a key research and development topic in the mineral processing industry. The gradual exhaustion of high-grade iron ore reserves, and rising consumer iron and steel demand globally necessitate efficient low-quality iron ore beneficiation to meet steelmaking quality requirements. This comprehensive review explores various beneficiation techniques for low-quality iron ore, focusing on conventional methods including comminution, froth flotation and gravity separation. This article discusses the principles, processes, and equipment used in these techniques and highlights recent advancements and research efforts in the field. This review also emphasizes the importance of effective beneficiation processes in enhancing economic viability, sustainable resource management, and environmental conservation. Furthermore, it presents a case study of iron ore deposits in Botswana, highlighting the potential economic growth and sustainable development that can be achieved by maximizing resource utilization through reductive roasting, followed by magnetic separation of iron ore using semi-bituminous coal as a reductant. Overall, this review provides valuable insights into low-grade iron ore beneficiation techniques and their significance in meeting the growing demand for high-quality iron and steel products.

1. Introduction

In recent years, low-grade iron ore beneficiation has evolved into a crucial subject of research in the mineral processing sector [1,2,3]. Low-quality iron ore beneficiation is an essential process in the utilization of iron ore deposits, particularly as demand for iron and its alloys continues to rise due to rapid industrialization and depletion of high-grade reserves [4,5]. Due to the steady degradation of high-grade iron ores (>60% Fe mass), low-grade iron ores (<60% Fe mass) are usually beneficiated to meet the quality requirements of the steel industry for maximum low-grade iron ore utilization [1]. Despite their inferior iron quality and high impurity levels, low-grade iron ores represent a sizeable portion of global iron ore reserves. According to a report conducted by the United States Geological Survey, the global resources contain around 230 billion tons of iron, with approximately 30% of the total resources estimated to be from lean-grade ores [6]. Effective and efficient beneficiation of poor-quality iron ores is essential for maximizing the utilization of these resources and meeting the growing demand for high-quality steel products worldwide. The mineralogy of iron ore and impurity levels determine the concentration routes of iron ores to obtain a high-quality iron ore concentrate. Effective beneficiation processes not only enhance the economic viability of low-grade ore deposits but also contribute to sustainable resource management and environmental conservation [7].

Despite its relative abundance in the Earth’s crust, iron is never found in its free elemental state and its occurrence is mainly in ores. These ores differ in chemical makeup and mineralogy influenced by their geographical occurrence. Iron ores can be categorized as high-grade and low-grade, which ultimately influences their processing routes. The economic grade of iron ore today, ranging from 44 to 64 wt.% Fe, is considered low-grade ores and only a few deposits can be considered high-grade (>60% Fe mass) [8]. High-grade iron ores are usually crushed, screened and/or directly fed as lump ore for iron extraction [9], whereas lately, an increasing amount of research [10,11,12] has focused on the exploitation of low-grade iron deposits due to the rapid depletion of high-grade deposits coupled with an increasing global demand for steel products and stringent legislation towards environmental pollution.

Figure 1 presents a typical processing flowchart of high-grade iron ores [9]. Iron ores with higher Fe% typically ranging from 65% to 70% are desirable direct feed for blast furnace and direct reduction processes [13]. Due to their high Fe content and favorable reduction kinetics, hematite and magnetite are the most preferred iron-bearing minerals [13,14].

Low-grade iron ores typically contain lower iron (Fe) content and higher gangue/impurities, which include quartz (SiO₂) up to around 30%, alumina (Al₂O₃) up to 20%, and other gangue minerals [15,16]. The definition of low-grade iron ore may vary depending on specific industry standards and requirements, and these ores are economically less valuable due to their lower Fe content. Low-grade iron ores are generally beneficiated to meet steel industries’ quality requirement (>65 Fe%) [17]. For example, in Botswana, the average iron grade is ~56% Fe, but the ores mostly contain high alumina and silica [18]. The USGS estimates that Botswana has 2 billion metric tons of iron ore reserves as of 2021 [19]. Some of the significant iron ore deposit localities in the country are listed in

Table 1. Significant iron ore deposits found in Botswana.

Reference	Name of Deposit	Location	Iron Content (wt.% Fe)	Comment
[20]	Ikongwe iron ore	Ikongwe, Near Shoshong Village	55–60	Considered low-grade ore (<64 wt.% Fe)
[18]	Matsitama deposit	Matsitama village, Central District	~56	Considered low-grade ore (<64 wt.% Fe)
[21]	Shakawe deposit	Shakawe, Northwest Region	59	Considered low-grade ore (<64 wt.% Fe)

and shown in Figure 2.

Several review articles on iron ore beneficiation have been published in the past, covering various aspects of iron ore beneficiation. Comprehensive reviews covered basic principles, process flows, and technological advancements in various areas, including comminution, magnetic separation, gravitational separation, and flotation [1,13,22]. A subset of the review articles explored and highlighted distinct challenges in upgrading such ores, including the efficient liberation of iron minerals, deleterious materials management, development of suitable and environmentally friendly beneficiation strategies, the impact of mineralogy and the geological characteristics on beneficiation [23,24]. Some review articles have taken a more localized approach, examining the beneficiation of iron ores within the context of specific regions or countries. For instance, Roy et al. and Das et al. focused on the beneficiation of Indian ores [25,26], while Araujo et al. covered the case of Brazil [14]; these reviews provided insights into the geological characteristics, resource availability, and technological adaptations for beneficiation in these regional localities.

While these existing reviews made valuable contributions to the understanding of iron ore beneficiation, the current review aims to build upon this knowledge by providing a more comprehensive, global perspective on the beneficiation of low-grade iron ores. The initial impetus for this review stems from the Botswana iron ore beneficiation project we are working on. This review aims to provide a broader understanding of the challenges and advancements in the field of lean- and low-grade iron ore beneficiation, drawing from experiences and research findings in various major iron-ore-producing regions around the world. By addressing conventional methods, recent developments, economic viability, and quality requirements, this article serves as a valuable resource for researchers, industry professionals, and stakeholders involved in the effective and sustainable exploitation of low-grade iron ore deposits [27].

2. Low-Grade Iron Ore Mineralogy

The mineralogy of low-grade iron ore varies depending on its source and geological formation and ultimately influences its concentration routes [14]. Primarily, the main challenge in the utilization of low-grade iron ores stems from their compositional makeup, which often includes high alumina (10%–15%) and silica content (4%–6%) [10]. These impurities and other deleterious elements (including phosphorus and sulfur) results in viscous slag formation, high coke rate, fuel consumption, and reduced productivity during steelmaking processes [28].

Common iron-bearing oxides in low-grade ores include hematite (Fe₂O₃), goethite $(\mathsf{\alpha }-\mathrm{F}\mathrm{e}\mathrm{O}(\mathrm{O}\mathrm{H}\left)\right)$ and traces of magnetite (Fe₃O₄), which usually consist of impurities such as quartz ($\mathrm{S}\mathrm{i}{\mathrm{O}}_2$), kaolinite $\left({\mathrm{A}\mathrm{l}}_2{\mathrm{S}\mathrm{i}}_2{\mathrm{O}}_5{\mathrm{O}\mathrm{H}}_4\right)$, gibbsite $\left(\mathrm{A}\mathrm{l}\right({\mathrm{O}\mathrm{H})}_3$) [29,30]. Kaolinite affects the liberation and separation efficiency of ores since it is a clay mineral, while gibbsite (aluminum hydroxide) contributes to high LOI, which affects the ore’s overall quality and processing kinetics [31,32,33].

3. Conventional Beneficiation Techniques

3.1. Comminution

Comminution in iron ore processing refers to the size reduction of solids from one average particle size to a lower average particle size using mechanical forces. This reduction can occur through various methods, including crushing, grinding, and other mechanical processes [34,35]. This technique liberates minerals from the ore matrix and makes it suitable for concentration processes. This process requires energy input to break down the ore into smaller aggregates and the response of the ore depends on its toughness and strength [35,36].

Crushing: Primary crushing is the first stage of comminution in iron ore processing. Lumps of run-of-mine (ROM) ore of typical size (diameter) 1–1.5 m are reduced to about 100–200 mm for rich iron ores [34]. Crushers exert pressure using firm surfaces to break down larger rocks into smaller ones.

Table 2. Various crusher types.

Crusher Type	Process Stage	Maximum Feed Size (mm)	Appropriate Maximum Output Size (mm)	Capacities (t/h)
Gyratory crusher	Primary	1500	200–300	1200–5000
Jaw crusher	Primary	1400	200–300	≤1600
Horizontal impact crusher	Primary/secondary	1300	200–300	≤1800
Cone crusher	Secondary	450	60–80	≤1200
Cone crusher	Tertiary	150	<30	≤1000

provides a summary of the various crusher types [34]. In primary crushing, both the jaw and gyratory crushers are used with the selection of equipment based on the ore grade, mineralogy, and hardness. Primary crushing is typically carried out in an open circuit and dry feed, and it reduces ROM down to acceptable sizes for conveyor transportation and secondary crushing [37].

The bulk of secondary crushing in iron ore operations is commonly performed using cone crushers. Roll crushers and impact crushers are also secondary crushers which find application in soft friable ores [38]. The reclaimed primary crushing product is fed to secondary crushing units. Secondary crushing operates with dry feed and produces material with a size of 30–50 mm ranging from the initial diameter size of 150 mm from primary crushing, suitable for grinding if operated in an open circuit.

Grinding: Primary, secondary, and tertiary grinding often requires rod mills, ball mills, or a combination of both to enhance mineral liberation and ore concentration of iron ores. Cone crushers can be used as tertiary crushers by means of installation in a closed circuit linking the secondary crusher and a ball/rod mill [34]. Grinding mills have the capacity to reduce feed particles of around 50 mm to an optimum liberation size between 40 and 300 µm [39]. Rod mills grind large particles preferentially, preventing the overgrinding of softer particles and therefore producing a smaller proportion of fine, overgrind particles [38]. Both semi-autogenous (SAG) and autogenous (AG) mills are commonly used across processing plants for grinding operations [40]. Autogenous mills break down ore by means of self-grinding of large ore particles without the need for a grinding medium. However, the variation in the ore’s abrasiveness and hardness may lead to an inconsistent final product due to a change in the ore’s breakage characteristics. Steel balls are added to aid the action of large ore particles during the grinding of the ore in semi-autogenous mills [38]. Figure 3 presents a combination of comminution techniques employed for liberation purposes before flotation [41].

Low-grade iron ores require extensive comminution (crushing and grinding), which aids in iron minerals’ liberation from the gangue matter, and ores are usually crushed and grinded to fine particles of up to 50 µm [1,42,43]. On the other hand, high-grade iron ores typically require less comminution since the iron minerals are easily liberated from the gangue matter [1].

Low-grade iron ores have different compositional characteristics and vary in minerals present and their abundance [44]. Different iron ore characteristics allow for varied liberation characteristics and comminution response and ultimately present different energy consumptions, which are dependent on the work indexes of associated minerals [45]. Understanding iron ores’ mineralogical characteristics and their work indexes is vital in comminution modeling and selective grinding [46,47].

Table 3. Bond work index of minerals associated with iron ores.

Mineral	Bond Work Index (kWh/t)
Hematite	12–14.3
Magnetite	11–12
Goethite	10
Quartz	13–15
Alumina	17–18

shows some of the minerals associated with low-grade iron ores and their relative grinding work indexes [48].

Particle size distribution (PSD) is a significant component in the comminution process, particularly in low-grade iron ore beneficiation [49]. Analyzing and understanding the PSD of the iron ores aid in grinding process control and determining the cut size for efficiency of other separation techniques, including magnetic separation and flotation [50]. The desired PSD can be achieved by adjusting grinding parameters such as feed rate, mil speed and grinding media size [35,51].

The PSD of iron ores significantly impacts both grinding efficiency and downstream concentration processes due to different cut size requirements for different techniques. The PSD cut size for flotation is wider, typically ranging from 10 µm to 150 µm, and requires prior removal of slimes (<10 µm) as they affect froth stability and consumption of reagents [52]. Magnetic separation is relatively effective for coarse particles (>150 µm), whereas techniques like reduction roasting require finer PSD cut size (<80 µm) to allow for improved chemical reactions [13,53].

3.2. Gravity Separation

This technique is suitable for ores in which the primary minerals have higher specific densities compared to their gangue matters [1]. Gravity separation processes rely on the density disparity between minerals to achieve concentration. Specifically, in the case of hematite ores, iron oxides tend to be denser than the gangue minerals, which primarily consist of siliceous compounds [54,55]. Specific gravities of common iron-bearing oxides and gangue minerals associated with low-grade iron ores are furnished in

Table 4. Showing specific gravity of iron-bearing compounds.

Name of Ore	Fe Content (%)	Specific Gravity
Hematite	70	5.0–5.3
Magnetite	72.4	5.17–5.18
Goethite	62.5	3.96
Limonite	60	2.7–4.3
Siderite	48.3	3.85
Iron Pyrite	46.6	4.9–5.2

[1].

Adequate feed preparation, which involves sequential steps such as crushing, screening, sizing, grinding and slime removal, improves the efficacy and effectiveness of gravity concentration. Slimes increase pulp viscosity and inhibit the appropriate sizing of crude fractions, ultimately affecting the machine separation efficiency [56].

The concentration criteria (CC) express the compliance of separating two minerals based on their specific gravities and if the quotient is more than 2.5, separation by gravity is easily applicable; when it is below 1.25, it becomes less feasible [57].

$$\mathrm{C}\mathrm{C}={\displaystyle \frac{{\mathrm{d}}_{\mathrm{H}}-{\mathrm{d}}_{\mathrm{F}}}{{\mathrm{d}}_{\mathrm{L}}-{\mathrm{d}}_{\mathrm{F}}}}$$

d_H refers to the heavy mineral specific gravity, whereas d_L and d_F refer to the light mineral and fluid specific gravity, respectively.

Jigging: Jigging is an old technique for gravity concentration that separates materials into three sections: lighter, medium, and heavy density [1]. In a basic jigging operation, a current of fluid (usually water) is repeatedly pulsated through a bed of ore particles, leading to the stratification of light and heavy particles according to their specific gravity, where heavier particles become concentrated at the bottom layer of the bed [58,59]. The jigging process is applicable for iron ore with particle sizes ranging between 30 and 0.5 mm. Sishen iron ore mine located in South Africa employs jigging technology for the beneficiation of ROM material that is considered waste, producing a saleable concentrate with 64% Fe content [60].

In jigs, typically ≤ 10.15 mm feed material is deemed suitable for jigging operations where finer particle separation is essential [61], with a greater separation efficiency when separating finer particle sizes due to improved iron mineral liberation from the gangue matter [62]. Figure 4 shows a typical jigging principle in separating particles based on ravity disparities [63]. Despite its versatility in the separation of both high- and low-grade ores, its efficiency is greater in well-liberated iron fines and low-quality ores [42].

Das et al. [25] studied the jigging operation in beneficiating low-grade iron ore. Utilizing a laboratory-scale jig, they reported that a concentrate with 66.51% Fe and 2.1% alumina was obtained from a feed encompassing 56.14% Fe and 7.8% alumina. To achieve these results, operating parameters including pulse frequency, amplitude, and feed particle size were optimized.

Jigging performance parameters

Feed particle size: Effective low-grade iron ore separation heavily relies on feed particle size optimization [64,65]. Numerous studies have shown that reducing feed particle size may enhance the liberation of iron minerals from the gangue, resulting in improved iron recovery and concentrate grade [44,49,66]; however, extensive grinding can also introduce slimes, which will result in high energy consumption in separation processes such as jigs, shaking tables and spirals [67].

Pulse frequency and amplitude: These parameters play a vital role during the jigging process of iron ore in achieving a high-quality concentrate [68]. Adjusting the frequency of pulsations in jigs impacts the particles’ motion during separation, while the amplitude of pulsations influences the differentiation and movement of particles in jigs [69,70].

Spiral: Spiral concentrators are commonly used in the production of mineral concentrates globally; these are also employed in iron ore fine beneficiation operations. The spiral process requires feeder material ranging between 1 and 0.03 mm (30 µm). Typically, this approach is appropriate for pulp densities between 25 and 30% solids [1]. However, with the high separation efficiency demand for iron ore fines, there have been a lot of developments in improving spiral concentration performance for iron ore beneficiation [37,38,39]. Iron ore fine treatment plants frequently use multiple-stage spiraling (rougher, scavenger, cleaner) circuits to obtain upgraded products with good recoveries. Spiraling products can be enhanced through magnetic separation to improve the quality of iron values for a saleable product [71].

Tripathy et al. [72] investigated the use of spirals in a low-grade iron ore concentration process. They obtained a concentrate with 63.4% Fe and 3.5% alumina from a feed with 54.4% Fe and 9.1% alumina. The study highlighted the significance of feed rate, pulp density, and spiral geometry on separation performance.

Spiral performance parameters

Feed rate and residence time: The residence time of particles within the separator is directly influenced by the feed rate [73]. Proper control of the feed rate results in optimal particle and spiral flow interaction and ultimately enhances separation efficiency [74,75].

Pulp density and fluid dynamics: In spiral concentrators, pulp density significantly influences the viscosity and flow characteristics of the slurry [73,76,77]. A higher pulp density increases the centrifugal forces acting on particles and this affects their trajectory within the spiral whereas a lower density alters the fluid dynamics, resulting in suboptimal concentration [78,79].

Spiral geometry: Variations in spiral concentrators designs (pitch, diameter and number of turns) impact the separation process, with different geometries affecting particles trajectory and stratification [80,81]. For heavy mineral separation, steeper spirals are often used for efficient separation, while wide-diameter spirals are employed to improve fine particle separation [82,83].

Shaking tables: Shaking tables are one of the most efficient equipment in processing an array of minerals with particle sizes ranging from 15 mm to 10–15 microns [2,83,84]. A shaking table’s capacity ranges between 0.5 tons/hour and ~1.5–2 tons/hour depending on the particle sizes of the material processed. As a result, it is common practice in the industry to set up tens of shaking tables either in a series or parallel to process large quantities of material [85,86].

Özcan et al. [2] reported the use of shaking tables for the beneficiation of a run of mine (R.O.M) sample assaying 21.91% Fe. The obtained results indicated that a high-grade iron concentrate (>65% Fe) was achieved by using −1 mm fraction. The study highlighted the significance of the table tilt angle, stroke length, and wash water flow rate in achieving optimal separation

Table tilt angle: The shaking table tilt angle influences the separation efficiency through particle stratification. Proper adjustment of the table tilt angle ensures efficiency in manipulating density differences [87,88].

Stroke length and particle movement: Longer stroke lengths enhance particle separation by allowing sufficient time for stratification. Shorter strokes may result in incomplete separation [89,90].

Wash water flow: Wash water dislodges impurities from the concentrate. Proper flow rate enhances the shaking table performance and results in high concentrate purity [82,91].

Centrifugal forces: Centrifugal forces have been successfully used to increase particle settling rate for both classification in hydro cyclones and dynamic heavy medium separation [92,93]. Over the years, various gravity separation units employing centrifugal forces have been developed, with the Knelson Separator and Falcon Concentrator attracting the most attention [94,95]. The Multi-Gravity Separator, which is a unit combining a centrifugal separator and shaking tables, and the Kelsey Centrifugal Jig, made of a standard jig technology and centrifugal force, are among the most used centrifugal concentrators worldwide [57,96,97,98].

Dey et al. [99] investigated the use of a Mozley Hydro cyclone in desliming an iron ore slime sample containing 59.22% Fe, 4.76% silica and 4.57% alumina. The study employed the use of different techniques, including an enhanced gravity separator to achieve an iron concentrate with 65% Fe. Pigot opening, feed pressure, and the diameter of the vortex finder and pulp density (10%) were studied as process parameters in the optimization of the desliming conditions.

Centrifugal concentrators performance parameters

Centrifugal Force: Centrifugal concentrators use rotational motion, creating a force field that separates lighter particles from heavier ones; therefore, centrifugal force optimization is critical in enhancing the separation of fine particles [100,101].

Feed rate: The throughput and separation efficiency are directly influenced by the feed rate. A higher feed rate increases the material flow, resulting in reduced processing capacity requiring optimized feed rate [102].

Fluidization water flow rate: To achieve efficient separation, adequate water flow is essential for maintaining bed fluidity within the concentrator, preventing particle settling and blockages due to clogging [103].

Table 5. Comparison of gravity concentration techniques reported for low-grade iron ores.

Type of Iron Ore	Equipment	Process Parameters	Results Achieved	Ref
Low-grade ore 56.5% Fe	Jigging (Denver mineral jig and Harz jig)	Feed size: 0.2–5 mm Water flow rate: 10 L/min Amplitude: 14.29 cm	63.7% with 78.6% recovery	[63]
BHJ ore with 36.27% Fe	Spirals	Feed size: 0.5–2 mm Spiral pitch: 12 mm Feed rate: 1.5 t/h	45.79% Fe with 64% Fe recovery	[26]
Iron ore slimes with ~58% Fe	Hydro cyclone	Feed size: 0.5–10 mm Pulp density: 20% Inlet pressure: 25 psi	64.2% Fe with 37.9% recovery	[104]
Ultrafine iron ore (~36% Fe)	Dense Medium Separation (DMS)	Feed size: 0.1–0.3 mm Pulp density: 40% solids Gas velocity: 6.37 cm/s	66% Fe, at 80% recovery	[105]

presents a comparison of the results obtained by various researchers using various gravity concentration techniques, including their performance based on specific parameters discussed above.

3.3. Flotation

Flotation techniques are often used to concentrate non-magnetic iron ores. Furthermore, they are frequently employed to improve the quality of magnetic ores [106,107]. Due to its capability to treat ores with complex mineralogy, ores with different densities and small particle liberation sizes, flotation has gained recognition as one of the predominant mineral separation processes [60]. In the flotation process, mineral recovery from the pulp takes place in three mechanisms: mineral particles attach selectively to air bubbles, followed by entrainment in the water passing through the froth, and, lastly, the aggregation of particles in the froth state [108]. Froth flotation is a selective process that separates hydrophobic and hydrophilic substances. Various reagents can exclusively alter the mineral surface’s hydrophobicity, enabling a wide variety of separation processes to be established [46,47,48].

Two main flotation routes:

Direct flotation: Anionic reagents float valuable minerals (including iron oxides) in direct flotation by attaching them to air bubbles. During anionic flotation, anionic collectors are responsible for floating and repelling the silica (positively charged) [22,52,107]. Strongly acidic pH levels naturally carry a positive charge on mineral surfaces other than silica, where magnesium and calcium cations preferentially attach to them. Activators are chemicals that provide the above-mentioned calcium or magnesium ions [22]. In practice, lime activates and floats silica gangues with fatty acids which act as collectors at pH levels 11–12, with starch lowering the iron-containing particles. The main benefits of anionic reverse flotation include decreased slime sensitivity and cheaper collector costs since fatty acids are readily available as paper industry waste products [109,110]. Some of the common anionic reagents include magnesium chloride (MgCl₂), oleic acid, sodium hydroxide (NaOH), and dextrin. Figure 5 presents froth flotation principle in which valuable minerals are targeted [110].

Reverse flotation: In reverse flotation, positively charged (cationic) reagents float gangue minerals like silica while preventing the flotation of iron oxides. Silica surfaces carry negative charges at pH levels above their point of zero charge; this allows reverse flotation to work across a wide range of pH values [15,22,109]. Alkaline pH levels are commonly employed to separate desired elements from silica; however, in the instance of hematite ores, a depressant is required to prevent hematite from floating. The cationic reverse flotation process was invented by the U.S. Bureau of Mines and is widely utilized in iron ore industries globally [111]. In this technique, amine collectors float silica gangue minerals like quartz, while starch depressants prevent the flotation of phosphate minerals in alkaline conditions (pH 9.5–10.5) [51,52,53].

Table 6. A comparison between direct and reverse flotation.

Aspect	Direct Flotation	Reverse Flotation
Flotation Target	Iron oxides are floated	Gangue minerals are floated with depression of iron oxides
Common Reagents	Anionic reagents (petroleum sulfonates, fatty acids)	Cationic reagents (primary amines, quaternary ammonium salt); sometimes, anionic reagents are used depending on the gangue
pH Modifiers (calcium hydroxide, sodium carbonate, sulfuric acid)	Creates favorable conditions for the flotation of iron oxides	Creates favorable conditions for the flotation of gangue minerals
Depressants (starch, dextrin, sodium silicate)	Prevents flotation of gangue minerals	Prevents flotation of iron oxides
Activators (copper sulfate, lead nitrate)	Not typically used	May be used prior to the addition of collectors to activate gangue minerals
Collectors (dodecanoic acid, sodium dodecyl, amines, fatty acids, xanthates, sulphate)	Aimed at increasing iron oxides hydrophobicity	Aimed at increasing the hydrophobicity of gangue minerals

compares and differentiates between direct and indirect flotation [107,109,112].

In India, China and Brazil, iron ore flotation is a commonly practiced separation technique with process control regarded as an integral part of flotation process operations. Mintek in South Africa developed an advanced flotation stabilization and optimization system, which was installed in Brazil’s Vale’s Cauè iron-ore-processing plant [113]. Performance analysis of the study showed increased iron recovery by 2.7% and decreased iron tailings by 1.2%.

However, the overall efficiency of the flotation process is heavily reliant on the mineral liberation characteristics and the gangue material present. For high-grade iron ores (>65% Fe), direct flotation is more suitable; the valuable iron mineral (hematite or magnetite) is floated using a specific collector, while the gangue minerals remain in the tailings. Direct flotation typically requires a finer grind size (80% passing 45 μm) to eliminate gangue from the iron minerals [42].

On the other hand, reverse flotation is commonly used in low-grade iron ores with the gangue minerals selectively floated using collectors, leaving the iron minerals in the tailings [107,109]. This process is essential in upgrading low-grade ores by removing impurities and increasing the iron content from about 38 to 60%. Furthermore, 80% passing 75 μm grind size is typically employed in reserve flotation; hence, it is more efficient in ore fines [114]. The existence of slimes in flotation increases reagent consumption and decreases flotation efficiency. Therefore, desliming is a critical step for efficient separation in iron ore flotation [115]. Table 6 outlines the difference between two main flotation routes. Some of the reported flotation and its performance studies are furnished in

Table 7. Successful iron ore flotation applications reported.

Ore Description	Flotation Technique	pH	Depressant (Dosage)	Collector (Dosage)	Frother (Dosage)	Equipment	Impeller Speed (rpm)	Particle Size; Pulp Density	Grade and Recovery	Ref
Hematite (TFe grade of 46.15%)	Direct flotation	10	Starch (600 g/t)	W-2 (150 g/t)	CaO (800 g/t)	Column cell	800 rpm	0.074 mm; 30% solids	66.7% Fe with 78% recovery	[116]
Hematite ore (~51% Fe)	Reverse flotation	11.5	Cornstarch (60 mg/L)	Sodium oleate (NaOl; 160 mg/L)	Methyl isobutyl methanol (20 mg/L)	Hallimond tube	900 rpm	<74 µm; 25% solids	59% Fe at 80% recovery	[117]
Iron slimes (~47% Fe)	Reverse flotation	9.5	Starch (1000 g/t)	Amine (55 g/t)	Dodecylamine	Column flotation cell	850 rpm	<32 µm; 10% solids	Recoveries: 41.7% (weight); 80% (iron)	[115]
Iron ore fines (~58% Fe)	Direct flotation	10.5	Sodium silicate (5 kg/t)	MIBC (2.5 kg/t)	Sodium oleate	Column flotation cell	1000 rpm	+74 µm; 10% solids	62% Fe at 59%	[52]

.

3.4. Magnetic Separation

Concentration in an ore deposit can be achieved via magnetic separation, which exploits differences in the desired mineral and gangue matter magnetic susceptibilities. Magnetic separators are often categorized into two groups based on their magnetic field strength: low-intensity (LIMS) and high-intensity (HIMS) [118].

Magnetic separation is a cheap, non-destructive, and easy method of concentrating iron-bearing minerals to almost mono-mineral levels, especially those found in varying quantities in silicates and clays [95,118]. Magnetic separation procedures are chosen based on a variety of processing criteria, including mineral composition, liberation size, and magnetic susceptibility, as well as production, marketing, and environmental concerns [94].

Magnetic susceptibility and intensity: Different minerals exhibit varying degrees of magnetic susceptibility, and magnetic separators exploit the differences in magnetic susceptibility [53,65]. The magnetic field can only attract paramagnetic and ferromagnetic minerals while repelling diamagnetic [119]. Both low- and high-intensity machines can operate on a dry-feed basis or wet-feed basis. Low-intensity magnetic separators operate with magnetic fields ranging between 1000 and 3000 gausses, whereas high-intensity magnetic separators use stronger fields up to 20,000 gausses [1].

Table 8. Magnetic susceptibilities of common magnetic iron-bearing minerals.

Minerals	Formula	Magnetic $\mathbf{Susceptibility} (\times {10}^{-6}, {\mathbf{m}}^3/\mathbf{k}\mathbf{g}$)	Fe Content (%)
Magnetite	${\mathrm{F}\mathrm{e}}_3{\mathrm{O}}_4$	1156	$\mathrm{F}\mathrm{e}$, 72.4
Vanadic titano-magnetite	($\mathrm{T}\mathrm{i}{\mathrm{O}}_2$, ${\mathrm{V}}_2{\mathrm{O}}_5$) ${\mathrm{F}\mathrm{e}}_3{\mathrm{O}}_4$	917	$\mathrm{F}\mathrm{e},$ 63.7; $\mathrm{T}\mathrm{i}{\mathrm{O}}_2$, 6.91; ${\mathrm{V}}_2{\mathrm{O}}_5$, 0.9
Hematite	${\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3$	0.6–2.16	$\mathrm{F}\mathrm{e},$ 69.94
Specularite	${\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3$	3.7	$\mathrm{F}\mathrm{e}$, 69.94
Limonite	$\mathrm{m}{\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3·\mathrm{n}{\mathrm{H}}_2\mathrm{O}$	0.31–1	$\mathrm{F}\mathrm{e}$, 48–62.9
Siderite	$\mathrm{F}\mathrm{e}\mathrm{C}{\mathrm{O}}_3$	0.7–1.5	$\mathrm{F}\mathrm{e}$, 48.3
Chromite	$\mathrm{F}\mathrm{e}\mathrm{O}·{\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_3$	0.62-0.89	$\mathrm{F}\mathrm{e}$, 25; ${\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_3$, 67.91
Pyrrhotite	${\mathrm{F}\mathrm{e}}_7{\mathrm{S}}_8$	57	$\mathrm{F}\mathrm{e}$, 63.53
Ilmenite	$\mathrm{F}\mathrm{e}\mathrm{T}\mathrm{i}{\mathrm{O}}_3$	0.35–5	$\mathrm{F}\mathrm{e}$, 33.33; $\mathrm{T}\mathrm{i}{\mathrm{O}}_2$, 52.66
Wolframite	$(\mathrm{F}\mathrm{e},\mathrm{M}\mathrm{n})\mathrm{W}{\mathrm{O}}_4$	0.5	$\mathrm{F}\mathrm{e}$, 15.60; $\mathrm{W}{\mathrm{O}}_3$, 76.58

shows the magnetic susceptibilities of common magnetic iron-bearing minerals that are recoverable using magnetic approaches [119].

Magnetic separators: Various types of magnetic separation equipment are used. This includes high-gradient, drum, and roll magnetic separators, and these devices exploit differences in magnetic susceptibility to separate minerals [119].

The Swedish Kiruna iron ore operations utilize LIMS separators for the beneficiation of a low-grade magnetite ore with ~60% Fe content [109]. Magnetic separation is operated both in dry and wet environments, although wet conditions are more prevalent. Figure 6 shows a drum magnetic separator being employed in wet LIMS [120]. This technique concentrates weak magnetic ores from non-magnetic materials, including hematite [26].

More than 90% of the global iron ore production is beneficiated by the magnetic separation process because the dominant iron ore minerals are para- and ferromagnetic [109]. Magnetite is the principal ferromagnetic mineral that is concentrated through low-intensity magnetic separators (<~0.3 T) because of its strong magnetic response [121].

Table 9. Successful studies reported on low-grade iron ore beneficiation by magnetic separation.

Study (Reference)	Initial Ore Grade (Fe%)	Technique	Process Parameters	Final Grade (Fe%); Recovery
1 [12]	43.5	LIMS (dry)	Magnetic intensity: 1000 gauss Feed size: 0.3–500 mm	67% Fe; 90% recovery
2 [31]	43.5	LIMS (wet)	Magnetic intensity: 1800 gauss Feed size: –0.075 mm Pulp density: 20.0% solids Feed rate: 10.0 kg/h	69.39% Fe; 87.3% recovery
3 [122]	~34	LIMS (dry)	Magnetic intensity: 1000 gauss Feed size: −0.074 mm	64.13%; 83.7% recovery
4 [73]	44.2	WHIMS	Magnetic intensity: 12,000 gausses Feed size: −200 µm Flow rate: 2.5 L/min Wash flow rate: 20 L/min	66.8%; 53.2% recovery

shows some of the successful studies in which magnetic separation was employed to concentrate lean-grade iron ores.

3.5. Reduction Roasting and Magnetic Separation

Reduction roasting, also known as magnetizing roasting, is the technique of transforming a material from weak magnetic to higher magnetic properties at a significant temperature ranging between 600 and 900 °C, and this entails the use of reductant [123].

In reduction roasting coupled with magnetic separation, the iron compounds found in the ore undergo conversion to form magnetite and are acquired via magnetic separation (low intensity); during this process, the ore absorbs heat, which results in fractures and ultimately aids in iron phases’ liberation during grinding [26].

The reducing atmosphere in iron ore roasting is commonly generated using carbonaceous reductants such as coal, sawdust and biomass [67,68,69]. Carbonaceous reductants provide carbon to the process, after which carbon combines with oxygen present in the air to make carbon dioxide, which then further reacts with carbon to form carbon monoxide. Carbon monoxide reduces iron phases into a more magnetic material.

The reduction of iron ore using a reducing agent, like coal, involves several sequential reactions: (a) diffusion of reducing gases through the boundary region; (b) diffusion of reducing gas interaction through inside-particle diffusion; (c) movement of Fe2+ and electrons towards the iron nucleus; (d) diffusion of the oxidized gas interaction through diffusion within particles; and (e) oxidizing gas diffusion across the boundary region. Reduction reactions that occur while iron ore is roasted using a solid carbon can be illustrated as follows [124]:

$${\mathrm{F}\mathrm{e}}_{\mathrm{x}}{\mathrm{O}}_{\mathrm{y}}\left(\mathrm{s}\right)+\mathrm{C}\left(\mathrm{s}\right)={\mathrm{F}\mathrm{e}}_{\mathrm{x}}{\mathrm{O}}_{\mathrm{y}-1}\left(\mathrm{s}\right)+\mathrm{C}\mathrm{O}\left(\mathrm{g}\right),$$

x = 1, 2, or 3,

$${\mathrm{F}\mathrm{e}}_{\mathrm{x}}{\mathrm{O}}_{\mathrm{y}}\left(\mathrm{s}\right)+\mathrm{C}\mathrm{O}\left(\mathrm{g}\right)={\mathrm{F}\mathrm{e}}_{\mathrm{x}}{\mathrm{O}}_{\mathrm{y}-1}\left(\mathrm{s}\right)+\mathrm{C}\mathrm{O}\left(\mathrm{g}\right),$$

where, y = 1, 3, or 4,

$${\mathrm{C}\mathrm{O}}_2\left(\mathrm{g}\right)+\mathrm{C}\left(\mathrm{s}\right)=2\mathrm{C}\mathrm{O}\left(\mathrm{g}\right).$$

Furthermore, the complete phase conversion from hematite to magnetite during reduction roasting can be depicted as follows:

$${3\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3+\mathrm{C}\mathrm{O}=2{\mathrm{F}\mathrm{e}}_3{\mathrm{O}}_4+{\mathrm{C}\mathrm{O}}_2$$

A typical schematic flowchart of iron ore reduction and magnetic separation is presented in Figure 7 [43].

Critical factors in the reduction roasting of iron ore can be defined as follows:

Temperature: During reduction roasting, temperature has a significant impact on the process. Optimal temperatures aim to balance reduction kinetics, phase transformations, and energy consumption. Lower roasting temperatures (<890 °C) tend to result in the production of considerable fayalite amounts and as the temperature increases, extremely finer hematite is more rapidly reduced to metallic iron, and fayalite amounts decrease sharply [125].

Residence Time: The time that the ore spends at the specified temperature during roasting is influential in the concentration process. Longer residence durations may result in improved reduction of iron oxides, but there is an upper limit beyond which excessive energy consumption occurs. Researchers have found that it is important to optimize both the temperature and time at the same time as they are mutually inclusive [125].

Reductant dosage: The amount of a reductant added to the iron ore significantly influences the reduction process as uniformly disseminated reductant powders improve the reduction kinetics and accelerate the reduction rate as the reductant sources the carbon, which is responsible for the reduction of oxides [126]. An efficient reductant dosage ensures efficient reduction while avoiding excessive carbon consumption. Recently, researchers have been exploring various reductant-to-feed mass ratios to find the right balance [127].

Several researchers have reported that the reduction roasting technique can be utilized in converting non-magnetic materials into magnetic materials through roasting in a reduced environment at higher temperatures (600–900 °C). Roasting iron ore at temperatures greater than 900 °C is unfavorable as it may result in particle infusion or, in some instances, the formation of paramagnetic wustite [49]. Successful investigations into the carbon-based reduction of low-quality iron ores followed by recovery via magnetic separation have been reported [47,49,50,52], with some of them presented in

Table 10. Successful studies on reduction roasting followed by magnetic separation of iron ore.

Study (Reference)	Feed Grade and Size	Reduction Process Parameters	Magnetic Separation Process Parameters	Final Grade (Fe%); Recovery
1 [7]	51.6% Fe −150 µm	Temperature: 950 °C Reductant: 3% coal Time: 53 min	Magnetic intensity: 3000 gausses	63% Fe; 79% recovery
2 [128]	56.2% Fe 75 µm	Temperature: 700 °C Reductant: 25% cow dung Time: 45 min	Magnetic intensity: 1800 gausses	64% Fe; 66% recovery
3 [129]	50.6% Fe 0.25–1 mm	Temperature: 1050 °C Reductant: 8% sodium bicarbonate Time: 80 min	Magnetic intensity: 0.08 T	90.87%; 95.8% recovery
4 [130]	45.23% Fe −10 mm	Temperature: 500 °C Reductant: ${\mathrm{H}}_2$ gas at flow rate; 1.5 L/min Time: 20 min	Magnetic intensity: 2000 gausses	59.6%; 90% recovery

.

3.6. Advantages and Limitations of Low-Grade Iron Ore Beneficiation Techniques

Iron ore beneficiation techniques have their advantages and limitations when it comes to ore processing, and these are crucial in selecting the most appropriate and suitable beneficiation technique.

Table 11. Advantages and limitations of iron ore beneficiation techniques.

Technique	Advantages	Limitations	References
Gravity separation	- Low cost - Environmentally friendly, does not require chemicals.	- Less effective for ultra fine ores - Low efficiency for ores with close density differences.	[59,110,131]
Magnetic separation	- High efficiency for magnetite ores - Can handle large volumes - Environmentally friendly - Can be conducted in both dry and wet environments - Versatile and can separate iron ore into multiple components	- Less effective for ores with weak magnetic properties ores - Requires significant energy input for generating magnetic fields - Less efficient in ultrafine dispersed ore particles	[15,53,131]
Flotation	- Effective for the treatment of carbonate-rich iron ores - Allows for the recovery of fine particles that may be lost in other separation methods	- Complex process, requiring careful control of various factors like pH, reagent type, and dosage - Desliming may be necessary to enable effective flotation, which can add to the process complexity and cost - It may not be as effective for ores with high levels of impurities or mixed mineral compositions	[22,106,114]
Reduction roasting	- Effective for converting and recovering high-grade iron value from low-grade resources. - Effective for complex and low-grade ores	- The process requires precise control of temperature, time, and reductant dosage - High energy consumption due to roasting	[32,43,132]

outlines these techniques’ advantages and limitations.

3.7. Proposed Methodology

The proposed project focuses on upgrading a locally sourced iron ore (59% Fe) [18] to obtain an upgraded concentrate that meets the required iron and steelmaking standards. This project intends to utilize the locally abundant semi-bituminous coal with 50% fixed carbon as a reducing agent in the reduction of the ore [133]. Botswana harbors over 212 billion tons of coal, which is currently only used for power generation; however, it could potentially be further employed for metallurgical purposes, in this case, the beneficiation of iron ores [133,134]. This reduces iron oxides present in the ore to a magnetic product, enhancing the iron content and improving its suitability for further processing [135]. Following reduction roasting, the upgraded iron-rich phase is separated from the gangue minerals using magnetic separation. The iron-rich phase magnetic properties facilitate this process, resulting in obtaining a concentrate with higher iron content. The proposed methodology for this project is furnished in Figure 8.

3.8. Reasons for Choice of Proposed Methodology

• Reduction roasting is effective in handling ultra-fine particles and complex mineralogy and eliminates impurities that are finely disseminated within the mineralogical assemblages, which are often difficult to eliminate by other methods.
• The presence of both hematite and magnetite in iron ores means that after magnetization roasting, the separation index is more optimized than with hematite alone.
• It is an energy-efficient process compared to other beneficiation methods, which often require more energy-intensive processes or the use of chemicals.
• Reduction roasting coupled with magnetic separation achieves higher iron recovery rates compared to gravity separation, flotation and direct magnetic separation alone.
• The process is effective in a wide range of ore compositions, offering flexibility in separation processes as it can be optimized to specific ore characteristics.
• Utilization of two under-utilized resources (iron ore, noncooking coal). The use of locally available reductant (semi-bituminous coal) and the potential for high recovery rates make reduction roasting economically attractive.
• The iron ore roasting process operates at moderate temperatures, which reduces energy consumption compared to more energy-intensive methods. The magnetic separation of roasted products is also carried out at low intensity, thus leading to a lower energy input.
• The use of semi-bituminous coal is environmentally friendly in comparison to chemical-inclusive methods, which, in turn, minimizes gas emissions and pollution.
• The process generates less tailings and waste compared to other beneficiation methods, reducing the environmental footprint of mining operations.
• Modern reduction roasting facilities are equipped with advanced emission control technologies to minimize environmental impact.

3.9. Project Contribution to Advancing Knowledge in Low-Grade Iron Ore Beneficiation

The proposed project intends to significantly contribute to the advancement of low-grade iron ore beneficiation in multiple ways, including the following:

• Optimization of reduction roasting parameters: Through this project, reduction roasting of local resource process parameters including temperature, coal-to-ore ratio, and residence time during reduction roasting will be optimized. This optimization process enhances the efficiency of the reduction process, leading to improved iron recovery and product quality and the ore’s economic feasibility is accessed.
• Characterization of upgraded concentrate: This project will provide valuable insights into the upgraded concentrate’s mineralogy and chemical composition, aiding in process optimization and product quality control.
• Environmental considerations: By utilizing abundant semi-bituminous coal with high fixed carbon content as a reductant in the oxide reduction process, this project explores an environmentally friendly approach to iron ore beneficiation. This contributes to the development of sustainable beneficiation practices that minimize environmental impact. Reduction roasting has reduced emissions and lower carbon footprint compared to traditional beneficiation methods like sintering.
• Technology transfer and implementation: The successful implementation of both roasting and magnetic separation techniques in this project demonstrates their practical applicability for upgrading locally sourced low-grade iron ores using locally abundant low-grade coal. This motivates potential technology transfer to industrial-scale operations, contributing to the broader adoption of efficient beneficiation methods in the mining industry which will also address the high iron demand.

4. Innovative Approaches in Low-Grade Iron Ore Beneficiation

As physical separation processes often yield limited results for low-grade ores, researchers are actively investigating alternative strategies to enhance iron content. Moreover, these studies emphasize the dynamic nature of this field, with continuous advancements expected in the future.

4.1. Microwave-Assisted Beneficiation

Microwave radiation is non-ionized electromagnetic radiation with frequencies ranging from 0 to 300 GHz. Nevertheless, the most common operating frequency worldwide is 2.45 GHz [136]. Through microwave treatment, iron ore particles can be selectively heated, producing thermal stress that enhances the elimination of gangue material from valuable minerals [114]. Studies by [82,83] highlight the potential of microwave-assisted techniques in enhancing iron ore beneficiation, improving resource utilization, and reducing energy consumption.

Agrawal et al. investigated the treatment of iron ore fines using a microwave furnace yielding 63.8% Fe concentrate, 99% recovery, and 87.4% product yield [137]. Nunna et al. investigated mineral transformations in a low-grade goethite-rich sample, with microwave heating leading to dihydroxylation and associated mineral changes that could potentially benefit ore beneficiation [138].

4.2. Thermal Plasma Technology

Thermal plasma processing is a varied field, with a wide range of applications including spray coating and elimination of hazardous waste [139]. Hydrogen plasma smelting reduction employs the hydrogen plasma arc generated between liquid iron oxide and hollow graphite electrode. The plasma state of hydrogen facilitates the reduction of iron oxides [140]. Thermal plasmas develop at pressures roughly 0.1 atm, and they are typically generated between two electrodes either by an AC or DC voltage or through a radiofrequency electromagnetic field [141]. Jayasankar et al. produced pig iron from red mud wastes utilizing plasma technology in an extended arc thermal plasma generator (35 kW DC) while employing fluxes and graphite with 99% fixed carbon [142].

4.3. Bio-Beneficiation

Researchers have explored bio-flotation, bio-flocculation, and bioleaching as feasible ways to recover iron from low-quality ores [143]. The recovery of minerals by microorganisms through bio-beneficiation provides a cost-effective, environmentally benign, and long-term solution. Iron ore deposits contain a variety of microorganisms that act as reagents in separating the desired mineral from associated impurities. Gangue removal is necessitated by several surface chemical and physiochemical phenomena, consequently enriching the valuable mineral constituent. In the context of iron ore, alumina and silica are eliminated through the use of heterotrophic microorganisms [144,145].

Some researchers [146,147] reported the use of bio-organisms, including saccharomyces cerevisiae, bacillus subtilis, and desulfovibrio desulfurizers in the processing of hematite ores. Microbially induced flotation and flocculation employ mineral-specific proteins and adapted cells to remove alumina, silica and calcite from hematite [148].

4.4. Utilization of Waste Materials

Metallurgical processes generate a million tons of mineral refuse annually, and presently billions of tons of this waste have accumulated worldwide. As steel demand rises and low-grade ores become more common, waste production is expected to increase [149].

In the quest for sustainable mining methods and resource conservation, the usage of waste materials produced during iron ore mining operations has gained significance. A study by [150] investigates the use of mine quarry dust and spoiled wastes (MSW) in the preparation of stabilized earth blocks and demonstrates how waste materials can be incorporated into civil construction.

At present, distinct methods for utilizing iron ore wastes have been developed in order to recycle valuable metals, including Fe, Ni, Cu and Co [151] to produce some building materials such as ceramics, admixture, and for other applications such as soil modification [98,99].

Furthermore, iron ore resources are becoming increasingly scarce in China due to the continuous consumption of mineral resources. Iron ore waste emits 130 million tons annually, with 2.5–3 tons emitted per concentrate ton. Provided that tailings retain approximately 11% iron, about 1.41 million tons of iron will be lost in tailings [152,153]. As a result, the recovery and usage of iron in iron ore tailings play a significant role in preserving iron resources. Currently, direct reduction and magnetizing roasting are the primary methods for recycling iron from tailings and other iron-containing waste [154].

5. Challenges Affecting Low-Grade Iron Ore Beneficiation

Low-grade iron ores typically have impurities, ultrafine particles, and complex mineralogy compositions. Conventional beneficiation processes have difficulties in efficiently recovering iron from ores.

5.1. Mineral Liberation

Low-grade ores usually have poor mineral liberation, making it difficult to extract minerals bearing iron from gangue. Various valuable mineral constituents need to be liberated from the associated matrix before any separation process can be attempted [155].

Quantifying mineral liberation is crucial for optimizing beneficiation processes. Poorly liberated minerals exacerbate limitations in the beneficiation process [156].

5.2. Environmental Concerns

Traditional beneficiation methods involve the use of chemical reagents, water, and energy-intensive processes. Efforts to minimize the environmental impact of traditional mining methods have made progress, but pollution remains an inevitable by-product. Ongoing research focuses on mitigation and amelioration strategies [24].

Sustainable alternatives are needed to minimize environmental impact. A review was conducted emphasizing the use of bioreagents derived from microbes to reduce chemical usage in processing and how bio-beneficiation methods have shown success in sustainable recovery [143].

5.3. Water Consumption

Water scarcity in many regions worldwide affects beneficiation operations and as a result, dry beneficiation technologies are gaining attention to reduce water consumption. Considering capital and operating costs, dry processing is less costly and more effective compared to dense medium processing and other techniques including flotation [157].

Dry beneficiation techniques involve advantages such as the removal of water and sludge flow and, in turn, simplify the technology employed through eliminating steps such as thickening and dewatering [158].

5.4. Tailings Management

During iron ore beneficiation, high volumes of tailings (solid waste, additives, water) are generated, and they pose a significant challenge in terms of environmental impact and effective utilization. These may contaminate water bodies, soil, and vegetation, and pose risks to ecosystems and human health [23].

Innovative tailings management strategies are essential to prevent environmental hazards [159]. Developing cost-effective and environmentally sustainable methods for resource recovery from tailings is needed [159].

6. Conclusions

• In conclusion, low-grade iron ore beneficiation plays a significant role in the usage of iron ore reserves and in meeting the increasing steel demand worldwide.
• This comprehensive review has highlighted various common beneficiation techniques, including comminution, gravity separation, flotation, and magnetic separation used in the beneficiation of low-grade iron ore.
• This review acknowledges the challenges posed by low-grade iron ore, including inferior iron quality and high impurity levels, but also recognizes the potential of these resources due to their significant global reserves.
• Additionally, a case study of iron ore deposits in Botswana has demonstrated the economic prospects and sustainable development opportunities associated with unlocking low-grade iron ores value.
• Further research and advancement in this field are essential to optimize beneficiation techniques and contribute to the advancement of the mineral processing industry.